Re: [Boost-users] shared_from_this - derived classes (yes, I googled)

Subject: Re: [Boost-users] shared_from_this - derived classes (yes, I googled)
From: Igor R (boost.lists_at_[hidden])
Date: 2011-10-02 03:29:12

> Well, I tried to get a trivial example and ended up having a working example. I
> suppose my problem is in the non-trivial part of my code :)
>
> Is this the correct way to do it?
>
>
> #include <iostream>
>
> #include <boost/enable_shared_from_this.hpp>
> #include <boost/shared_ptr.hpp>
>
> //--------------------------
> class A : public boost::enable_shared_from_this<A>
> {
> public:
>
> Â  Â ///
> Â  Â typedef boost::shared_ptr<A> SmartPtr;
>
> Â  Â ///
> Â  Â static A::SmartPtr Create()
> Â  Â {
> Â  Â  Â  Â A::SmartPtr instance;
>
> Â  Â  Â  Â // Check arguments if any
>
> Â  Â  Â  Â // Create an instance of this class
> Â  Â  Â  Â instance.reset(new A());
>
> Â  Â  Â  Â return instance;
> Â  Â }
>
> Â  Â virtual ~A()
> Â  Â {
> Â  Â }
>
> protected:
>
> Â  Â A()
> Â  Â {
> Â  Â }
>
> };
>
> //--------------------------
> class B : public A
> {
> public:
>
> Â  Â ///
> Â  Â typedef boost::shared_ptr<B> SmartPtr;
>
> Â  Â ///
> Â  Â static B::SmartPtr Create()
> Â  Â {
> Â  Â  Â  Â B::SmartPtr instance;
>
> Â  Â  Â  Â // Check arguments if any
>
> Â  Â  Â  Â // Create an instance of this class
> Â  Â  Â  Â instance.reset(new B());
>
> Â  Â  Â  Â return instance;
> Â  Â }
>
> Â  Â ///
> Â  Â virtual ~B()
> Â  Â {
> Â  Â }
>
> Â  Â ///
> Â  Â B::SmartPtr Foo()
> Â  Â {
> Â  Â  Â  Â A::SmartPtr temp = shared_from_this();
>        B::SmartPtr me   = boost::shared_dynamic_cast<B, A>(temp);
>
> Â  Â  Â  Â return me;
> Â  Â }
>
> Â  Â ///
> Â  Â void Bar() const
> Â  Â {
> Â  Â  Â  Â std::cout << "Success!" << std::endl;
> Â  Â }
>
> protected:
>
> Â  Â ///
> Â  Â B()
> Â  Â  Â  Â :
> Â  Â  Â  Â A()
> Â  Â {
> Â  Â }
> };
>
> //--------------------------
> int main()
> {
> Â  Â B::SmartPtr b1 = B::Create();
> Â  Â B::SmartPtr b2 = b1->Foo();
>
> Â  Â if( b1 != b2 )
> Â  Â {
> Â  Â  Â  Â std::cout << "they aren't equal." << std::endl;
> Â  Â  Â  Â return 1;
> Â  Â }
>
> Â  Â b2->Bar();
>
>
> Â  Â return 0;
> }

Your example compiles and works well.
(Actually, you don't need shared_dynamic_cast here,
static_pointer_cast would be well enough.)